Multiple hearth furnace



March I8; 1930. E. J. FowLl-:R ET AL 1,751,142

MULTILE- HEARTH FURNACE Filed'March 8, 1928 nu :p

BY WMA/W attorneys iaatentecl Mar. l, 193@ EDWARD J'. FO'WLEB., DECEASED, LATE 0E' REDWOOD CITY, CALFORNIA, BY EDETH MARY FOVVLER, EXECUTRIX, 0F REDWOOD CITY, CALIFGRNIA, AND DUDLEY BMRD, OF BERKELEY, CALIFORNIA, l.ASSIGNOBS TO NECHOLS COPPER COMPANY, 0F NEW YORK, N. Y., A CORPORATION 0F NEW YORK MULTIPLE HEARTH FURNACE 'application fue@ March e, ieee. serial no. 260,032.

. This invention relates to multiple hearth roastingfurnaces and more particularly to methods and means for controlling temperature conditions at the various hearths of such furnaces. Also the invention as to certain of its phases relatesA to the construction and operation of furnaces having a substantially greater number of hearths than has heretofore been embodied in furnaces of this general type.

The objects of the invention include the provision of furnace construct-ions of the class indicated, and also methods of operating such furnaces, which will be dependable, relatively simple and efficient under various conditions, and in which the treatment of various kinds and grades of material may be accurately controlled.

Various further and more specific objects, features and advantages will clearly appear from the detailed description given below taken in connection with the accompanying drawings which form a part of this specification and illustrate merely by way of example one embodiment of the apparatus of the invention.

The invention consists in such novel features, arrangements and combinations of parts as may be shown and described in connection with the furnace herein disclosed by way of example only Aand as illustrative of a preferred embodiment, together with such novel methods and steps of processes as may be described herein.

The drawing comprises a vertical sectional view, partly broken away, through a furnace vcomprising one embodiment of the invention.

The furnace a's illustrated may be of the same general class as that shown in numerous patents to J. B. F. Herreshof, as for example No. 976,175 ofi-.November 22, 1910, and may incorporate if l.desired various iniprovements such as for example the improved shaft and rabble arm'construction shown in the copending application ofl Dudley Baird, Ser. No. 140,230, led October 8, 1926.

A plurality of vertically spaced or super-l posed hearths is indicated and designated respectively by the numerals 1 to 12. These damper v20.

hearths may be surrounded and supported in the conventional manner as by a cylindrical furnace wall 13. A rotatable and internally cooled central shaft 14 extends vertically up through the center of the furnace and is provided with rabble arms as at 15 and 16. ln the embodiment shown, two oppositely directed rabble arms are provided to cooperate with each hearth area in the usual manner. Suitable rabble teeth as at 17 are provided along each of the rabble arms for advancing the material being treated successively over each hearth down through the furnace.

While in the drawing, 12 hearths only are indicated for simplicity, it will be understood that various features of the invention are applicable alike to furnaces having a number of hearths in the neighborhood of 12 and to furnaces having a substantially larger number of hearths, for example as many as 25.

The central shaft 14 as here illustrated, may be provided with an internal conduit as at 18, the rabble arms being also provided with inner conduits of any desired well known form communicating with the conduit 18, whereby cooling llind such as air carried by the conduit/,18 may be allowed to pass through the conduits of the various rabble arms, and thence back into an annular space 19 between the conduit 18 and the walls of the shaft 14. rlhe cooling fluid for example may be introduced through the usual adjustable 'damper intake at the end of the conduit 18 at the bottom of the furnace and the same fluid or a portion thereof, after having circulated through the various rabble arms, may be discharged from the top of the shaft 14 as through an adjustable At various of the hearths, or if desired at all or substantially all of the hearths, the

shaft 14 may be provided with sockets or attaching means as at 21 designed to receive heat absorbing or radiating arms as at 22. The sockets 21 as shown may beconveniently located intermediate the rabble arms 15 and- 16. The radiating units 22 may be made communicative through the sockets 21 with the cooling Huid conduit 18 at their inlet ends and with the annular space 19 at their outlet ends7 whereby a circulatory path is provided through the radiating units, thus permitting control or alteration of the temperature conditions on hearths which are provided with such radiating means. In certain processes it may be desirable to maintain some of the hearths at a relatively low temperature, or combustion conditions may be such as to require a considerable cooling eHect on certain hearths. This may be generally accomplished by using one 0r two o f the radiating units as at 22 over such hearths, or if these prove insufficient to accomplish the desired cooling, leither a greater number of these units may be applied at each hearth, or similar but larger units as at 23 may be used. As indicated at 21, the supporting sockets for the radiating arms may be more or less closely spaced so as to provide for the desired number of' arms at each hearth. Although the radiating arms as here shown comprise a single conduit, it will be understood that various other forms and shapes of radiating units might be utilized to secure the desired cooling effect. Also it will be understood that the invention is applicable equally to various furnace constructions well known in the art,

having central shaft arrangements otherv than the particular double concent-ric wall construction shown. 1

If for particular processes it is found to be unnecessary to use radiating units as above described at certainhearths, the socket provisions such asat 21 may be still provided for manufacturing convenience and standardization of shaft parts, the unused sockets being then 'covered either temporarily or permanently by cover plates as at 24.

At other hearths, the lowermost hearths for example, it will rmt only be found to be undesirable to provide cooling means with many processes, but `the efficiency of the furnace may be improved by raising the temperature at such hearths. For this purpose hot air arms as at 25 may be provided to fit, if desired, sockets such-as at2l interchangeabl with the radiating units, so that sections o the shaft 14 may be standardized and still have provision for either type of arm, The hot air arms 25 are made communicative With'the annular space 19 s'o as to dischargeffa part of the air therefrom directly on Vtothe material under treatment at the hearths. -The air or other fluid medium thus discharged Willof course be preheated to a considerable extent by reason of having previousl passed through the radi. ating unit and t e rabble arm cavities. A convenient means is therefore provided for reducing the temperature on certain hearths to the extent desired and for transferring the heat thus acquired in the cooling-medium, to other hearths where the eciency of operation may be enhanced by an increase over the temperature which would otherwise prevail. If desired, for certain roasting operations the furnace temperatures at the various hearths may be substantially equalized in this manner.

When hot air arms as at 25 are used in lieu of radiating units at the sockets 21, the openings communicating with they interior sha-ft conduit 18 may be closed 0H as by plugs as at 26; similar plugs of course may also be used whenever the plates 24 are necessary.

In some instances it is desirable to provide at certain hearths7 particularly at the lower hearths, a greater amount of preheated air than can be admitted by the arms 25. In thatevent, one of the rabble arms at such hearths may be replaced by a relatively large ht air arm as at 27 To achieve efficient roasting conditions, it is generally desirable to locate the openings of the arms 25 at points where the preheated air will engage the falling material as it passes from one hearth to the next. For example, the arms 25 at hearth #10 may be placed so that the preheated air-impinges directly upon the material dropping from the hearth #9 through the central hearth opening 28. The arms 27 if desired, may be somewhat larger and longer than the arms 25 so as to widely distribute the preheated air over the hearth areas.

As to the design and constructional details of other parts of the furnacel not specifically referred to herein, the usual practice may be followed as in the construction of other well known furnaces of this general type.

The above described radiating or heat absorbing arms are particularly useful in many roasting operations when placed at the intermediate hearths, since thereis often a tendency for the intermediate hearths to become overheated as a result of the rapid chemical actions taking place in the materials under treatment When they arrive at the mid-portion of the furnace. On the other hand, as

tible or oxidizable substances in the upper or intermediate hearths. This' invention therefore provides a convenient means for trans1 ferring the excess heat of the intermediate hearths to the lower hearths where such heatv 'is often needed to give the ores or other material a complete and nal roasting.

rEhe heat absorbing arms embodying this i invention should of course be clearly distinguished from the mere use of air cooled rabble arms in which the function of the cir- .as to form, number and arrangement, in

order to insure a uniform flow through the furnace of the material under treatment, on the other hand the heat absorbing arms at each hearth may, of course,'be made independent of such arms on the other hearths,

. as to form, number, and arrangement. The

cooling arms provide a cooling effect sub-- stantially in excess of any normal cooling effect arising from the use of the usual air cooled rabble arms, since the heat absorbed from the furnace through the necessarily relatively thick walls of the rabble arms is small as compared with the heat whichgmay be transferred throughcoolin arms as at 22 designed particularly for t at u rpose.

Although for convenience and) for obtaining substantial uniformity of cooling effects throughout the area of the hearths it is desirable to arrange the .rabble arms and cooling arms alternately as shown, it will be understood that approximately equivalent results might be obtained by other arrangements or by providing the radiating units as substantially unitary structures in conjunction with the rabble arms.

According to this invention, the circulatingcooling fiuid serves as many as three functions; namely, the necessary cooling of the rabble arms and shaft is accomplished,

temperature conditions throughout the furnace may be equalized or controlled with a wide range of flexibility, and a source of preheated air is provided at certain hearths for insuring a very effective lsupply of oxidizing fluid sufficient for proper completion of the roasting processes. At the same time the heat available throughout the furnace is.

substantially larger number of hearths with a consequent correspondingly large number of material drops or places where the ma.- terial drops from one hearth to the next through the ascending hot oxidizing gases. At these material drops the multitudes of nely divided particles have ample opportunity for sufficient contact with the oxidizing gases notwithstanding the degree of fineness of the material. However, as the number of hearths is increased, the control of temperature conditions throughout the furnace becomes more difficult, but any difficulties in that respect may be readily met by the heat transferring means providedin the manner above described. With many roasting operations it is desirable to provide relatively cool hearths at the top of the furnace (the top four or six hearths forexample), and also a number of relatively cool hearths at the very bottom of the furnace, (as many as four or six hearths) and this is ordinarily permissible only where the number of hearths is increased to in the neighborhood of 12 or more. According to our invention these cooler hearths may be maintainedat temperatures in the neighborhoolhof 800 F. to 1000 F. for example.

On the other hand, in certain roasting operations as above indicated, it is desirable to have'hot discharge calcines and in connection with acid manufacture, particularly chamber acid, it is desirable to have a hot gas discharge and cool cinder discharge. With some sulphide ores the free sulphur ignites at the top hearth, resulting in high temperatures at the upper hearths. It is obvious, however, that a furnace with a large number of hearths as above described, particularly if equipped with the heat absorbing arms and hot air arms,'will permit operating conditions satisfactory for all of these various processes and at the same time provide a sufficient number of material drops to insure rapid and thorough rocessing notwithstanding the fineness of t e material.

In the treatment of zinc ores Where the furnace is fired on the lower hearths, furnaces as above described are particularly desirable in that oxidation may be gradually carried out on several or numerous of the hearths instead of largely on one or two hearths, as has generally occurred in practice. Furnaces embodying this invention are adaptable to a wide variety of other uses such as calcining of fullers earth, filtering clays, fltrol, limestone, dolomite, mercury ores, soda compounds, copper, iron, zinc, tin, antimony and arsenic ores, drying operations, etc. In these various operations the temperature conditions within the furnace may be so con- .'trolled as to Asupport combustion from the ores or material treated, or of course, the furnace may be fired externally.

While the invention has been Adescribed with respect to certain particular preferred examples whichV give satisfactory results, it will be understood by those skilled in the art after understanding the invent-ion, that various changes and modifications may be made without departing from the spirit and scope of the invention and it is intended such changes 'and modifications.

What is claimed as new and desired to be Ytl'nerefore in the appended claims to cover all secured by Letters Patent of the United States is:

1. A roasting furnace comprising a plurality of superposed hearths, a rotatable shafteXtending vertically of the furnace and carrying rabbling means, and additional means also carried by said rotatable shaft at one or more of the intermediate hearths for absorbing heat therefrom, said additional means providing a greater heat absorbing capacity at said intermediate hearths than is provided inthe other hearths.

2. A roasting furnace comprising a plurality of superposed hearths, a rotatable shaft extending vertically of the furnace and carrying rabbling means, and additional means also carried by said shaft for absorbing heat at one or more of the intermediate hearths and transferring such heat to one or more of the lower hearths, said additional means providing a greater heat absorbing capacity at said intermediate hearths than is provided in the other hearths.

3. A roasting furnace comprising a multitude of superposed hearths, 12 or more in number, surrounded by a furnace wall, a rotatable air cooled shaft extending vertically ofthe furnace and carrying air cooled rabbling armsv cooperating with the various hearths for advancing material under treatment successively over the various hearths down through the furnace from top to bottom, and additional means carried by said sha-ft for absorbingheat in the cooling air therein at one or more of the intermediate hearths. V

4. A roasting furnace comprising a multitude of superposed hearths, 12 or more in number, surrounded by a furnace Wall, a rotatable air cooled shaft extending vertically of the furnace and carrying air cooled rabbling armscooperating ,with the various hearths for advancing material under treatment successively over the various hearths down through the furnace from top to bottom, additional means carried by said shaft for absorbing heat in the cooling air therein at one or more of the intermediate hearths, and means also carried by the shaft for discharging some of the air thus heated on to hearths Where higher temperatures are. desired. l

5. A roasting furnace comprising a plurality of superposed hearths, a rotatable shaft extendin vertically of the furnace and carrying rabbling means, said shaft' and rabbling means havmg communicating cavities providi'n a circulatory path for cooling fluid, soc et means independent of the rabbling members provided on said shaft at various hearths, and heat absorbing means detachably connected at said sockets and communicating with said circulatory path therethrough.

6. roasting furnace comprising a pluralranma absorbing means.

7. A roasting furnace comprising a plurality of superposed hearths, a rotatable shaft extending vertically of the furnace and carrying pluralities of rabbling arms cooperating with each hearth, and heat absorbing arms also carried by said shaft at one or more hearths, said heat absorbing arms and said rabbling arms being arranged alternately in spaced relationship around the shaft.

8. rllhe method of operating a multiple hearth roasting furnace having air cooled rabble arms Which comprises utilizing a part of the cooling air to absorb substantial quantities of heat in excess of that absorbed through'said arms and the arm supporting means at one part of the furnace and to convey such heat to another part of the furnace.

9. The method of operating a multiple hearth roasting furnace having air cooled rabble arms which comprises utilizing a part of the cooling air to absorb substantial quantities of heat in excess vof that absorbed through said arms and the arm supporting means at the mid-portion of the furnace and to deliver such heat at the lower part of the furnace.

10. A roasting furnace comprising a plurality .of superposed hearths, a rotatable shaft extending vertically of the furnace and carrying rabbling means, said shaft and rabbling means havingcommunicating cavities providing a circulatory path for cooling fluid, cooling fluid discharging arms also carried by said shaft, and said shaft having socket means for interchangeably receiving said rabbling means and said arms.

In testimony whereof We have signed our names to this specification.

EDITH MARY FOVLER, Eeeutm' of the Zwet willv and testament of Edward J. Fowler, Deceased.

DUDLEY BAIRD. 

